Tufa, or Tuff, is volcanic rock (it’s also the name for limestone concretions in water).  Having more than 50% tuff in a rock makes it ‘tuffaceous’ – lovely word that.

It all comes from the explosion of Taupo – or more accurately the hole that is now Lake Taupo, 1800 years ago.  Which was unimaginably huge.  The forests were burned to a cinder, and the ash cloud fell back onto the surrounding land, forming mounds of what is now extremely rich soil.  Hence all the grass and cows.

You can see the bubbles in the rock in the first photo, and the depth of the ash in the second.  And how it’s all mixed with stones, like concrete, in the third.